In evolved UMTS Terrestrial Radio Access Network (E-UTRAN) system several cell transmission bandwidths are possible e.g. 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz etc, see 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS) radio transmission and reception”. Also, different transmission bandwidth can be used in neighboring cells on the same carrier frequency. As a result cells with the same center frequency, sometimes termed intra-frequency cells, may have different transmission bandwidths. Irrespective of the cell transmission bandwidth, a user equipment (UE) is usually required to perform measurements on the neighboring cells. It is important that the measurement reports from different cells are consistent and can be used by the network to execute reliable handovers, i.e. correct handover decisions.
Furthermore, mobility support is one of the fundamental features of any cellular systems. In E-UTRAN the mobility is to be supported both in idle mode and in connected mode. In idle mode the UE in E-UTRAN is required to perform autonomous cell reselection based on some network signaled parameters. This allows the network to control UE mobility behavior in the coverage area to some extent. Also, the UE shall be able to perform cell reselection within the same frequency layer (intra frequency cell reselection), between different frequency layers (inter-frequency cell reselection) and also between E-UTRAN and other systems such as UTRAN (inter-RAT cell reselection).
In connected mode the network shall direct the UE to perform handover to a particular cell, which may belong to the same serving frequency (intra-frequency handover) or to another frequency (inter-frequency handover). Though this decision is taken by the network, it's primarily based on the UE measurement reports. As in case of cell reselection, the UE in connected mode shall also support mobility (i.e. handovers) within the same frequency layer, inter-frequency handovers and inter-RAT handovers.
The cell reselection and handovers are generally based on one or more downlink measurements. These measurements are done on some known reference symbols or pilot sequences.
Another important aspect of the mobility is the identification of the UE position or geographical location. This allows the UE to get an access to location based services, e.g. map reading. There are several different types of positioning methods. In some of the methods the UE identifies its location based on one or more neighbor cell measurements that are also done on some known reference symbols or pilot sequences.
Neighbor cell measurements are performed by the UE on downlink channels in the serving as well as on neighbor cells for example on reference symbols or pilot sequences. Unlike other measurements such as Channel quality indicator (CQI) which is done on Transmission Time interval (TTI) level (e.g. 1 ms), the neighbor cell measurements are performed over longer time duration, typically in the order of few 100 ms. Neighbor cell measurements can be broadly divided into two main categories:                Radio related measurements        Timing related measurements        
The radio related measurements are used to take handover decisions and allow a UE to do cell reselection in idle mode. Depending upon a particular mobility scenario more than one downlink measurement may be required to ensure robust mobility decisions. For instance coverage, interference and load in the cell would impact the cell change/handover decision.
In E-UTRAN the major mobility measurements are done on reference symbols, which are sent with a certain pattern defined in time and frequency. Furthermore the pattern is repeated in every slot (i.e. 0.5 ms). The agreed downlink channel measurements are described in 3GPP TS 36.214, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer; Measurements”:                Reference symbol received power (RSRP)        E-UTRA Carrier received signal strength indicator (E-UTRA Carrier RSSI)        Reference symbol received quality (RSRQ); RSRQ=RSRP/RSSI        
RSRP is measured over the downlink reference symbol whereas carrier RSSI is measured over all the sub-carriers (i.e. sub-carriers containing reference symbols and data).
In E-UTRA, as stated above, the neighbor cells, even operating on the same carrier frequency (i.e. intra-frequency cells), may employ different transmission bandwidth. Nevertheless the downlink measurements from all the cells operating over the same carrier frequency in at least part of the coverage area should be performed over the same measurement bandwidth to ensure consistent measurement reports. It is known that measurement bandwidth can be signaled by the serving cell to the UE.
In order to prevent ping pong during cell change, one important characteristics of the neighbor cell measurement is to properly filter out the affect of fading. The averaging in time domain and in frequency domain can be traded. However, longer time domain filtering may cause unnecessary delay in obtaining measurement reports and this could adversely affect the mobility performance.
In connected or active mode the inter-frequency RSRP, RSRQ and RSSI are performed by the UE during idle gaps, which are repeated periodically. Similarly E-UTRA measurements (e.g. E-UTRA FDD measurement) done by a multimode terminal when operating under another technology (e.g. WCDMA, E-UTRA TDD etc) are to be performed during gaps. A WCDMA UE will perform E-UTRA measurements during compressed mode gaps.
A UE has a relatively short time to perform IF and IRAT measurements. The actual time depends upon configured gaps. For instance denser gaps (i.e. more frequent gaps) would lead to shorter overall measurement period as the UE can obtain sufficient samples in relatively shorter time. Therefore it may be sufficient to measure over shorter measurement bandwidth e.g. over 5 MHz rather than 10 MHz bandwidth. However dense pattern may not be in use all the time because it adversely affects user throughput.
Therefore when infrequent gaps are used the measurement bandwidth needs to be adjusted, i.e. larger measurement bandwidth may be desirable. By increasing the measurement bandwidth the measurement period can be reduced thereby retaining good mobility performance.
There are three main deployment scenarios:                Homogeneous bandwidth deployment: all cells have same bandwidth        Heterogeneous bandwidth deployment: cells have different bandwidth        Cells on borders of homogeneous and heterogeneous bandwidth cells        
The above mentioned deployment scenarios are not expected to change very frequently.
However, there are several events, which require more frequent modification of the measurement bandwidth more such as:                Change in measurement gap pattern (e.g. periodicity changed from 20 ms to 140 ms or vice versa).        A new base station is added or removed.        Change in cell planning: when cell transmission bandwidth of one or more of the cells is upgraded or downgraded.        
It is important that network is able to use a consistent and optimal value of measurement bandwidth even if there following changes occur: modifications or changes in network configuration, changes in radio resource management strategies etc.
Hence, there exists a need for a cellular radio system that enables a more frequent modification of measurement bandwidth.